UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Leadville I°x2° quadrangle, Colorado: a pre-assessment by Alan R. Wallace , Steve Ludington , Tom G. Lovering , D. L. Campbell 1 , J. E. Case2 , V.J.S. Grauch1 , and Daniel H. Knepper, Jr. Open-File Report 88-0074 1988 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Denver, Colorado -Menlo Park, California CONTENTS Page Preface................................................................. 1 I. Executive summary................................................. 2 II. Geology........................................................... 5 III. Geochemistry...................................................... 9 IV. Geophysics........................................................ 12 V. Mineral resource assessment....................................... 15 VI. Proposed work plan................................................ 21 VII. Appendices 1. Bibliography.................................................. 1-1 2. Geochemical element anomaly descriptions...................... 2-1 3. Interpretation of geophysical data............................ 3-1 4. Deposit model critical characteristics........................ 4-1 FIGURES Figure 1. Index figure................................................. 3 2. Map showing districts, wilderness and wilderness study areas, and geochemical tracts.............................. 10 3. Map showing tracts for Climax and porphyry-type deposits..... 18 4. Map showing tracts for polymetallic hydrothermal deposits.... 19 5. Map showing tracts for sandstone-hosted deposits............. 20 TABLES Table 1. Mining districts in the Leadville quadrangle.................. 4 2. Geochemical anomalies......................................... 11 3. Resource assessment........................................... 16 4. Base- and precious-metal mining areas......................... 17 PREFACE This document presents a proposal and work plan for an evaluation of the mineral resource potential of the Leadville I°x2° quadrangle in west-central Colorado under the Conterminous United States Mineral Resource Assessment Program (CUSMAP). The authors of the report assembled available published and unpublished information and data germane to the geology, geochemistry, geophysics, and economic mineral deposits in the quadrangle. The team then identified specific topical studies that, when completed and incorporated with existing information, would provide the data necessary to adequately evaluate the mineral resource potential of the Leadville quadrangle. The work plan covers 5 years 4 for data acquisition and 1 for preparation of the final report as well as a preliminary period of time during which existing data can be evaluated and some new data could be collected. Owing to the lack of adequate data for resource assessment, this report does not attempt to provide, nor should it be construed to be, a preliminary resource assessment of the quadrangle. However, the available data suggest that the quadrangle has a high resource potential for a number of important commodities. I. EXECUTIVE SUMMARY The Leadville I°x2° quadrangle is situated in west-central Colorado in the heart of the southern Rocky Mountains (fig. 1). The area combines a complex geologic setting with an impressively diverse and bountiful resource potential. A Conterminous U.S. Resource Assessment Program (CUSMAP) evaluation of the quadrangle by the U.S. Geological Survey (USGS) would provide an ideal opportunity to refine assessment techniques and increase our scientific understanding of mineral deposits. The proposed study area is underlain by a lithologically and structurally complex Proterozoic crystalline basement, exposed in deeply incised uplifts, which is overlain by a thick accumulation of Phanerozoic sedimentary rocks. Mesozoic and Tertiary plutons and volcanic rocks are exposed throughout the quadrangle. Stream sediment samples were collected throughout the quadrangle as part of the National Uranium Resource Evaluation (NURE) and Forest Service and Bureau of Land Management Wilderness programs. The resulting data are in part reflections of known mineralized areas. However, they also identify numerous areas of interest outside of those areas, as well as suggest different model types within recognized districts, which should be evaluated further during a full-scale resource assessment. Unfortunately, molybdenum, which is present in the world-class Climax-type deposits, was not analyzed for during the NURE program. Geophysical data emphasize the complexity and diversity of the study area. Aeromagnetic and gravity maps suggest that, where covered by Phanerozoic rocks, the crystalline bedrock, where not exposed, is present at relatively shallow depths in much of the eastern half of the quadrangle. In addition, the geophysical data suggest the presence of deep intrusions. Remote sensing and radiometric maps point to regions within the study area where low-temperature ground-water processes could have concentrated minerals. The Leadville quadrangle contains three of the most productive precious- metal districts in the United States, Leadville, Aspen, and Gilman, as well as Climax, the world's largest molybdenum deposit. More than 39 other districts are present as well (table 1). There are also indications for the possible occurrence of a wide variety of other resources, including syngenetic metal deposits, industrial minerals, and fuels. Expected Benefits Scientific The knowledge of the geologic setting is relatively good, and the quadrangle contains an impressive diversity of mineral deposit types. Within this context, therefore, the Leadville quadrangle offers an exceptional opportunity to actively concentrate on topical studies related to ore deposits and their geologic context. The studies should be interdisciplinary and should incorporate all available facilities and capabilities. Interaction between the CUSMAP study and current and proposed projects would be mutually beneficial to all projects. The scientific products would also fuel future research in the area and region. .109 10B____ 107______KM IDS 104. 103 102 I I 1 40 Owiw Cgtbondolrs. Fryinqpon Rtvtr BoMlt Figure 1. Index map showing the location of the Leadville quadrangle and selected geographic and geologic features. Broken lines in southeast part of quadrangle outline gravity low described by Tweto and Case (1972) Table 1. Summary of Mining Districts, Leadville Quadrangle, Colorado DISTRICT COUNTY DEPOSIT TYPE Alicante-Birdseye Lake Al Alma Park Bl, B2, E Ashcroft Pitkin B2 Aspen Pitkin Bl, B2 Avalanche Pitkin B2 Breckenridge Summit Al, A2, B2, D, E Brush Creek Eagle C Buckskin Park A1.B1 Burns-McCoy Eagle E Climax Lake A1,A2,D Consolidated Montgomery Park Al Frisco Summit Al Upper Fryingpan Pitkin Al Fulford Eagle A1,B1 Gilman-Redcliff Eagle Al, Bl, B3 Granite Chaffee A1,E Green Mountain Summit A2,B2 Holy Cross Eagle Al Homestake Eagle Al Homestake Peak Lake Al Horseshoe Park Bl Independence Pitkin A1,A3 Leadville Lake A1,A3, B1,E Lenado Pitkin Bl, B2 Lincoln Gulch Pitkin A3 Mosquito Park A3,B1 Richmond Hill Pitkin Bl Rifle Creek Vanadium Garfield C Rifle - Elk Creek Garfield Bl, B2 Rock Creek (Crystal River) Gunnison B2 Sacramento Park Bl Snowmass Pitkin C St Kevin - Sugarloaf Lake Al Tenmile Summit B2 Tennessee Pass Lake A2,B1 Twin Lakes Lake A1,A3 Upper Blue River Summit A1,B1,B2,E Weston Pass Park Bl Yarmony Routt C Key to Deposit Types; Al - Au- and Ag-bearing veins in Precambrian rocks. A2 - Au-, Ag-, and base-metal veins in Tertiary intrusive rocks. A3 - Au- and Ag-bearing veins in Tertiary volcanic rocks. Bl - Ag-Pb-Zn veins in Paleozoic carbonate rocks. B2 - Base-metal vein and replacement deposits in sedimentary rocks C - Sandstone-type deposits in clastic sedimentary rocks. D - Disseminated porphyry and stockwork deposits. E - Placer deposits. Economic The preliminary mineral resource assessment indicates that the Leadville quadrangle has a high potential for undiscovered resources of a variety of metals and other important commodities. A full-scale assessment would delineate specific areas for known deposit types, and it could possibly identify deposit types heretofore unknown in the area. A CUSMAP resource assessment could make an enormous economic contribution both locally and nationally. Political The CUSMAP study would draw upon or interact with other U.S. Geological Survey (USGS) projects and programs. These include: * More than fifteen Forest Service and Bureau of Land Management (BLM) wilderness areas that have been studied within the quadrangle; * Projects that are currently in progress or are being proposed that would pertain to resource assessment of the quadrangle; and * Current DAT projects that include studies of the Leadville district, northern Sawatch Range mineral deposits, and the geochronology of central Colorado intrusive rocks and mineral deposits. In addition, the strong research interest in various aspects of the quadrangle shown by universities throughout the country invites active interaction with academia. II. GEOLOGY The geology of the Leadville I°x2° quadrangle represents more than 1.8 billion years of active tectonism, extensive plutonism, and cratonic sedimentation. During that time, geologic processes created substantial accumulations of mineral and energy resources, some of which have been tapped and others that undoubtedly await discovery. The geology of the quadrangle is shown in Tweto